analysis of a digital elevation model in ArcMAP

welcome everyone to this new lesson and no remote sensing techniques in this lesson we will concentrate on the questions on to analyze a digital elevation model and especially not analyze DMS derived by the shuttle radar topography mission also called srtm and yeah with some kind of pixel size of about 90 meters and first of all we will change the system today because this is not as you can see there was not add as imagine it is the art map arc arc info from a story interface you can see here in the version 10 and for this lesson you will need some digital elevation model you can get from the global and cover facility also known by the URL and to cover dock by going there you will need to use the SD interface or ESD interface please check out my other videos how to get some data from this GUI first of all let me explain you some things about arcmap so you have the layout or the data view here where you can see the Russa and then you have some kind of list of layers you will have a result here maybe when you're starting it and maybe the most important one is the arc toolbox you can use and let us start with e with just a new project so there's a new project and we will add some data here this is more or less now the dialogue had to where to choose your your data and this is the original data this is a processing limit level float finished I think and as you can see here just by creating this new race or I think this rasta to the view you will see some grayish picture a blackish surrounding and by using the identify button you can check the values you maybe know that as inquire cursor and add as imagine as you can see outer space years minus 32,768 68 with which is the lowest possible number in the sign 16-bit format and there are also some original values so elevation values in meters above sea level as you can see you're regarding the ellipsoid wgs84 you will have some Heights about 1300 or 2000 meters and an upper left there somehow picks up to 3000 4000 meters and there are some lower areas here and yeah as you can see this image doesn't show anything which is quite useful so first of all we will search for function which is called oh no we don't search for it it takes too long so you will have these toolbox and there are a lot of love things to use and especially the data management tools by looking into Norris and there are some properties you can recreate or recalculate statistics of the layers because the statistics in this in this image is distorted because of the highest and lowest values and we will recalculate the statistics but clicking on it choosing the ocelots that we would like to calculate ignore values is here - 2768 we will add this value to the to the to the list click OK the otras is created and as you can see here the results are calculated and there we go Pedrosa data set let this to the to the image I'm removing that and you can see much more of the image so you have below as values here 26000 which are probably in the in the area here somewhere let's check out identify yeah really so normally they should be there somewhere so but yeah we are now having some kind of first impression of the digital elevation data what is digital the elevation data in our area of interest and this is percent so you can also arrange the color ramp here so just by using this maybe invert to have the brownish things in in the higher areas and the greenish color in the lower areas but you can also check the properties and therefore this is quite important to see so we have the color ramp you can check by using minimum maximum together really a good value but this was not so successful so [Music] let's go back to this Sukhram specification no standard deviation which provides pass information here and we can also use this value we have just ignored we can we can use this value as background color and by using this we only have our area of interest or we have good values so this is a first step so now we have a digital elevation model everything is clear so we are having some kind of low and high values and you can identify each value by using the identifier part once again so there are several raters maybe in on that kind of data because this is a topography you can calculate the slope on every point which is similar to the gradient so the steepest slope of any slopes and any directions and how to do that but it's quite quite easy to do so just go on the spatial analyst tools maybe and also you 3d analyst tools special analyst tools and therefore the surface and you can see the possible function see and there's the slope function so we have an input dresser which is probably more or less than this sotn value you can also use a drop-down menu and we will create a new russell data set which is out called output rasa in our in our folder sunday we have and there's more less slope and degrees dr. there we go we will use decrease instead of percentage person draws and we don't have to change the set factor let's go straight forward sometimes you will see directly the the output of disable plus function and i have to add it this for my own so as you can see ya they have the green areas with nearly no slopes with slope values or really small slopes small scales I don't know low values and slope and you also have areas where you have higher values and slope especially in the upper northwest impart but one important thing to know is just look under ston this area here you may be you can see there's some striping in the in the image this is due to the sensor so you can arrange this by making some kind of neighborhood analysis or Fogo focal mean analysis on that and recalculate this digital elevation model otherwise just be prepared to see some features like that like the swiping and the digital elevation model if you were not able to use a function because of some kind of extension problem you can also go to customize extensions and you just have to check these buttons to activate so everything looks fine so far and we'll now go ahead as you can see here maybe I our areas or hi areas here more or less really steep and what we will do now is we will calculate a hill shade what is that so it's creating from servers are by considering the illumination source angle and shadows you can also use a tool help to get some idea about the function and how does it work and also the parting scripts that could be used to create the same result so therefore we also need any progress and be prepared not to use the slope or something like that so we will all concentrate on the SRTM values and we also have to change the change the folders so this is the aspect I know it's a mood and the altitude as it is maybe calculates shadows to get a more plastic or view one at all to get an idea about the topography so as you can see you that's this area this is all brownish so you don't have any differentiation between the higher parts and the lower parts because it's all the same the same color so the main main or the yeah the the best part on this on the search headers then you will get an idea about the about the aspect about the about the topography and where are the rich lines so by using this you will have somebody's about 0 which are probably directing south east I think and and then angle of steeper than 45 degrees and also half here this methods of 2054 which are more or less inclined in the angle of 45 degrees and looking into northwestern directions so by adjusting the display button here and also the transparency to 50% maybe and by unchecking this one you would get a very good idea about the topography area so you can see the colors of the height but also the hood shading which are which is laying above so you will get a really good view on the topic on topographic features so this is hope side and we have created a slope volume and maybe you don't want to use this kind of classes here in the slope in degrees you can also change that by using this layer properties and checking stretched instead of classified you just have to arrange the color chart here so we will go from green to red which is quite nice and we have to invert it because we are except more expecting green areas with no slopes or with less and concepts and as you can see you have the lower values of zero and 89% 89% is really rare so it normally occurs you on the edge because you will have this missing values and therefore you will get these are hardcore slopes on local I will call them and here we have these highest values you can also check all layers identified once more and as you can see if these the middle little cell was 1157 but a corresponding other sides are - 30 mm so that is the problem why it's doing that at calculation on the edges so yeah this is no slip we have outside what is left so we need an aspect where is the slope looking to if we also need the in progress as a set which is the SH M datum then we'll create a new layer which is called a speck dr. go ahead straightforward no difficulties and doing that it's quite fast at their stupid display and this is now a little bit more now well I think it's it looks like some kind of psychedelic feature but let me explain T you will have to be the aspect is telling you where the slope is heading to so in red you can see the noir thanks northern exposed slopes which are looking into north and directions and then you have the area of 25 degree 20 to 5.5 degrees up to 60 7.5 degrees these are the slopes looking into northeast interactions and so far so you have a pre classified image in Aris in ArcGIS which is telling you whether with the slope is looking to because yeah some kind of hydraulic features are correspond to them so let's assume that you are having having only North on only only difference between north and south and expose it slopes and of course the south and expel slabs will draw a much faster after a rain event and northern exposed slopes even have this differences here so and you can see also the second possibility so you have to make area here and connected to the value of minus 1 because their flat area so they don't have any aspect so there's aspect we have the epitome what is left it's the second derivative so the first derivative which is also called the slope would say to you how far is how fast movement of maybe a whole slide or Rockville so you can you can calculate that by maybe really thinking about about the pressure on the ground but yeah let me explain it like how far how fast is a movement on on a given slope so if it's deeper it's faster so what we are is the second derivative which is also called the curvature and for the curvature you also need the SOTN value you will create a curvature S sub which is the overall curvature now we'll explain it from our data so it's the curvature turf and that factor okay we are now normally using meters and therefore we don't need any set factorization but there's some two different output curve which arises here you can you can create so the first one is a profile curvature so how is a movement is it accelerating or is it breaking more and this sticks out decelerating so if it's a convex profile curvature you will have accelerating movement if it's a concave curvature you will have decelerating or braking of mass movement so this is profile curvature look at the nose look at the profile of your nose and you will have some kind of feeling what is convex and concave so then you have the output plan curvature asar which is in another direction so this is the let me just copy that it's a plan curvature and plan curvature is saying what's giving you an idea about the about the convergence or divergence of the mass movement so if you have if you have a convex slope you have divergent movement of Annie of sediment fluxes or fluxes as well and if you have a converge or convergent plan curvature converge know if it's gone no concave forms or divergent convex forms are convergent so the mass movement is concentrating on an area so these are two different curvature faults you will create here you will just click OK into the results I created here and you'll now have a look here on the profile curvature let this to disappear as you can see the values are too far away so we will create minimum maximum stretch and we will edit the highest value to one and the lowest value to minus one so and now you can see we will have convex and concave forms let's have a look into the help function mmm hopeful well thank you ok a value of zero is indicating a flat surface which is yeah quite what we have accepted and but a negative value indicates that the surfaces awkwardly convex at that so that means that the mass movement is accelerating and may be converging and opposing that if it's if this value is positive you will have positive you will have a concave form at this song so let's go back and do that so you can just create this kind of profile so far and yeah that's for the moment I think if you would like to make map out of it just go straight for route check out my other videos we can see how to make arc more how to make maps without map thank you for watching goodbye

Channel: Digital Geography

Views: 166,340

Rating: 4.8859472 out of 5

Keywords: SRTM, DEM, DGM, how-to, tutorial, ArcMAP, remote sensing, analysis

Id: poFzniaKogU

Length: 19min 10sec (1150 seconds)

Published: Tue Jun 07 2011